IgM antibodies against cysticercus antigens were measured by enzyme-linked immunosorbent assay (ELISA) in 133 serum and 126 cerebrospinal fluid (CSF) samples from patients with active neurocysticercosis (NCC), in 61 serum and 32 CSF samples from patients with inactive NCC, and in 556 serum and 449 CSF samples from patients with other neurological disorders. For diagnosis of active NCC the test showed 50% sensitivity with 70% specificity in serum and 87% sensitivity with 95% specificity in CSF. We concluded that the use of the ELISA with serum is not reliable for diagnosis of NCC and therefore cannot be used routinely for the detection of cases or epidemiological studies. Conversely, ELISA used with CSF is highly dependable for detecting all forms of active NCC. The possible explanations for the discrepancy between serum and CSF results are discussed.